If we can learn anything from networking jokes, no amount of guns will make UDP TCP, just like forcing Yemenis to accept legitimacy based on your definition of the need for stateful intervention to prevent stateless chaos and terrorism (the biggest fad word of the decade) and will not work (I would not be surprised, knowing my history of ancient Greece, if the terrain and disconnected government are not so uncommon, see Afghanistan also).
I agree on the should-can dichotomy. The problem is that I was under the impression the should was important in the betterment of society than the can, and that has recently changed. But maybe because I was raised by lawyers, I was taught the should was more important the can, hence the idea of constitutional powers. I am under the impression that is the outrage with PRISM/FISA/general government malfeasance these days: like a cop who badgers someone he pulls over and does not follow his legal obligations, the USG in Yemen, in signals intelligence, in everything to be honest, does what it can and worries about the should later, and will find any excuse in the should category that is exceptional to justify a "can" they knew to be a "cannot." It is disgusting.
It is ok: my time abroad taught me all governments are shams, and we best tolerate them just to make them pleased with themselves. The USG is like all other bullies, and any government bully must be convinced in its total allegiance of the flock or it must (can) flex its muscle even though it knows it should not. Unfortunately when the bully beats too many people, they gang up and trounce on him.
Sorry, end rant. Not meant to be directed at you. Your last point is really good, but it defines exactly what makes me want to be Scandinavian. I do not want to support my government even tacitly anymore.
This distinction is not irrelevant. In our system of government, courts decide "can" while the political process decides "should." But we have a tendency of equating the two, and responding to every instance of "shouldn't" with "you can't do that!" "Can" Obama pursue terrorist suspects into Yemen with force? Yes! Should he? Who knows.